tunicate


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tunicate

(to͞o`nəkĭt), marine animal of the phylum ChordataChordata
, phylum of animals having a notochord, or dorsal stiffening rod, as the chief internal skeletal support at some stage of their development. Most chordates are vertebrates (animals with backbones), but the phylum also includes some small marine invertebrate animals.
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, which also includes the vertebrates. The adult form of most tunicates (also called urochordates) shows no resemblance to vertebrate animals, but such a resemblance is evident in the larva. The most familiar tunicates are the sea squirts, or ascidians (class Ascidiacea). Adult sea squirts are sedentary, filter-feeding, cylindrical or globular animals, usually found attached to rocks, shells, pilings, or boat bottoms. The soft body is surrounded by a thick test, or tunic, often transparent or translucent and varying in consistency from gelatinous to leathery. The tunic (for which the tunicates are named) is secreted by the body wall of the adult animal. It is composed of cellulose, an almost unique occurrence of that material in the animal kingdom. Two siphons project from the animal's body; water enters the incurrent siphon at the top of the body and leaves the excurrent siphon at the side. Food particles are filtered from the water by the pharynx, which occupies most of the body, and are then passed into the digestive system. Some species reproduce by budding, resulting in the formation of colonies of sea squirts, joined at their bases by slender stalks or embedded in a slab of common tunic material. In addition, nearly all species reproduce sexually and are hermaphroditic. The free-swimming larva, called a tadpole, has a muscular tail and is similar in appearance to a frog tadpole. The larva has the characteristic chordate features also found in the embryos of vertebrates: a dorsal, hollow nerve cord; a stiffening rod, or notochord; and gill slits leading into the pharynx. The tadpole eventually settles and undergoes a drastic metamorphosis into the adult form. A common solitary sea squirt of both coasts of North America is the slender, yellow, transparent Ciona intestinalis, about 2 in. (5 cm) tall. The sea peach, Tethyum pyriforme, is a round, peach-colored sea squirt found from Maine north. Sea grapes are clusters of the greenish colonial squirt, Molgula manhattensis, common from Massachusetts south. Golden stars are colonies of various Botryllus species; the bright yellow individual animals are grouped in starlike clusters in a flat, encrusting, greenish tunic. Asplidium species form colonies of minute animals embedded in a gristly tunic; chunks of such colonies, typically dead, bleached, and often washed ashore, are known as sea pork. There are two other groups of tunicates, both found in the plankton of open oceans. The salps (class Thaliacea) are barrel-shaped tunicates, open at both ends; they swim by muscular contractions that force water through the body. The related pyrosomes form free-floating, translucent and bioluminescent colonies known as sea pickles. The larvaceans (class Larvacea) retain the larval form, with a tail and a notochord, as adults. A commonly held theory maintains that vertebrates evolved from animals like the larvaceans. Larvaceans have no tunics, but secrete gelatinous containers, called houses; these are used to filter food from the water and are continuously discarded and replaced. Tunicates are classified in the phylum Chordata, subphylum Urochordata.
References in periodicals archive ?
It thus appears that there may be multiple sites for ascidian blood (hemolymph) production, in particular in colonial tunicates.
Tunicates (n = 71), gastropods (n = 29), polychaetes (n = 27), and arthropods (n = 47) were processed and then tested using qPCR.
2006) Tunicates and not cephalochordates are the closest living relatives of vertebrates.
Planktonic tunicates (Chordata, Tunicata) of the RTMA "Evrika" in the southwestern Atlantic Ocean.
Clavanins, [[alpha]]-helical antimicrobial peptides from tunicate hemocytes.
The tunicate is just one of many wonderfully weird animals that live in the dark depths of the sea.
This debris may bury small, sessile organisms such as anemones and tunicates, and may restrict movement or distribution of organisms that live on rock surfaces (chitons, snails, and limpets).
Cytotoxicity reactions in the solitary tunicate Styela plicata.
Trees of GCLM and GS showed that the tunicate cluster, represented by Botryilus schlosseri and Ciona intestinalis, is always positioned close to the cephalocordate + vertebrate clade (Figs.
Kuanoniamines, Kuanoniamines A, B, C, and D: pentacyclic alkaloids from a tunicate and its prosobranch mollusk predator Chelynotus semperi, J.
In contrast, Jumeri & Kim (2011) reported high concentrations of valine and threonine in the solitary tunicate Styela clava from Gangwon Province, South Korea.
Cellulose nanofibers have been characterized and extracted from algae (Valonia) (32), wood (33), tunicate (34), sugar beet (35), brown algae (Oomycota) (36), bacterial and commercially available microcrystalline cellulose (13).